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Rectal Masses 865

Rectal Masses Client Education
Sheet
VetBooks.ir Diseases and Disorders

Malignant masses:
BASIC INFORMATION
metastasis, additional mass lesions
• Cachexia • Abdominal and thoracic radiographs: for
Definition • ± Dehydration, signs of abdominal pain
Tumors of the distal gastrointestinal (GI) • Sublumbar lymphadenopathy (may be Advanced or Confirmatory Testing
tract can be benign or malignant. The most palpable per rectum) suggests neoplasia. • Abdominal ultrasound: pelvis can interfere
common benign tumors are adenomatous • Rectal adenocarcinomas can spread circum- with imaging distal colon
polyps; others include leiomyoma, fibroma, ferentially or radially through bowel wall • CT: optimal structural evaluation
plasmacytoma, ganglioneuroma, inflammatory as pedunculated (mid-to-distal rectum), • Endoscopy/proctoscopy/colonoscopy
pseudopolyposis, and idiopathic eosinophilic ulcerative, cobblestone, or infiltrative masses. ○ Evaluate primary lesion location and
masses. The most common malignant rectal ○ Sedated rectal exam may be required to determine whether other lesions exist.
tumor is adenocarcinoma; others include palpate deeper infiltrative masses. ○ Biopsy samples obtained by this method
lymphoma, leiomyosarcoma, hemangiosarcoma, ○ Circumferential or stenotic lesions are usually small and superficial, which
extramedullary plasmacytoma, mast cell tumor, (colon to midrectum) suggest adenocar- can result in an incorrect diagnosis.
melanoma, and fibrosarcoma. cinoma. • Incisional/excisional biopsy: recommended
• Lymphoma can be discrete or diffusely ○ Depending on mass location, full-thickness
Epidemiology infiltrative. biopsy by laparotomy or partial-thickness
SPECIES, AGE, SEX biopsy by rectal eversion technique may
Benign masses: Etiology and Pathophysiology be necessary.
• Adenomatous polyps: more frequent in • Malignant transformation of benign masses ○ Adenomatous polyps are composed of
males occurs in 20%-50% of dogs, more commonly branching lamina propria covered by
• Benign GI masses are rare in cats. in masses that have been present for longer abnormal epithelial tissue that is continu-
Malignant masses: durations. ous with normal rectal mucosa.
• More common in older dogs ○ Carcinoma in situ refers to polyps that ○ Leiomyomas arise from the outer smooth
• Adenocarcinoma: higher incidence in males undergo carcinomatous change, invading muscle and lack mucosal involvement.
• Adenocarcinoma in cats: median age of 12.5 the intestinal lamina propria and submu- • Misdiagnosis common with cytology
years cosa but not the basement membrane,
and have a metastatic potential. TREATMENT
GENETICS, BREED PREDISPOSITION • Hematochezia is usually not seen with
Benign masses: leiomyomas and leiomyosarcomas because Treatment Overview
• Collies and West Highland white terriers they do not involve the mucosa. Surgical excision is the treatment of choice
are predisposed to adenomatous polyp • Chronic bleeding may result in anemia, for most rectal tumors except lymphoma.
formation. thrombocytopenia, and hypoproteinemia. The surgical approach is determined by
• Rottweilers and purebred, large-breed dogs • Smooth muscle tumors may cause tumor type and location. Strict aseptic
are predisposed to eosinophilic masses. hypoglycemia. technique is required because of the risk of
• Medium- to large-breed dogs appear predis- • Plasmacytomas may cause hyperproteinemia infection associated with rectal flora; systemic
posed to leiomyomas. and monoclonal gammopathy. perioperative antibiotics include gentamicin
Malignant masses: or amikacin plus second- or third-generation
• Medium- to large-breed dogs are overrepre- DIAGNOSIS cephalosporin or metronidazole. Postoperative
sented. antibiotic administration is controversial, but
• German shepherds and poodles are predis- Diagnostic Overview antibiotics should be continued if contami-
posed. Type of tumor is suspected based on appear- nation has occurred. Enemas should not be
ance and location. Definitive diagnosis requires administered preoperatively because liquid
Clinical Presentation biopsy and histopathologic analysis. Endoscopic feces may increase the risk of surgical site
HISTORY, CHIEF COMPLAINT exam can localize the primary lesion and help contamination.
Clinical signs include dyschezia, hematochezia, determine if other lesions are present.
hemorrhage, tenesmus, abnormal feces, ema- Acute General Treatment
ciation, anal biting/licking or scooting, and Differential Diagnosis • Surgical excision
diarrhea. Leiomyomas and adenocarcinomas • Perineal hernia ○ Rectal eversion and submucosal resection
may cause signs secondary to extraluminal • Perianal neoplasia may be used for noninvasive masses such
obstruction, such as vomiting, diarrhea, and • Colonic adenocarcinoma (p. 30) as polyps or carcinoma in situ.
weight loss. • Perianal gland hyperplasia ○ Benign polyps can be excised down to the
• Anal sacculitis level of the muscularis, ligated, or removed
PHYSICAL EXAM FINDINGS • Anal sac neoplasia by electrocautery.
Benign masses: • Rectal pythiosis ○ Cryosurgery can be considered for treat-
• Principal physical abnormalities are found • Benign rectal stricture ment of polyps and has been used for local
on rectal palpation. excision of adenocarcinomas; evidence for
• Adenomatous polyps can be single (80%) Initial Database this method is limited.
or multiple (20%) and raised, sessile, or • CBC, serum biochemistry profile, urinalysis: • Resection and anastomosis of larger lesions
pedunculated. paraneoplastic leukocytosis can occur with ○ Anal, ventral, dorsal, or lateral approach,
• Most commonly found at the distal rectum adenomatous rectal polyps; eosinophilia, depending on mass location
and anorectal junction neutrophilia, hypocholesterolemia, and hypo- ○ Rectal pull-through technique
• Leiomyomas are intramural and well- albuminemia may be seen with idiopathic ○ Caudal midline celiotomy with pubic
circumscribed. eosinophilic masses. symphysiotomy or ischial pubic flap

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